Minimally-invasive intracardiac ablation is the treatment of choice for various types of arrhythmias. To perform such treatment, the physician typically inserts a catheter through the vascular system into the heart, brings the distal end of the catheter into contact with myocardial tissue in areas of abnormal electrical activity, and then energizes one or more electrodes at or near the distal end in order to create tissue necrosis.
U.S. Pat. No. 6,059,780, whose disclosure is incorporated herein by reference, describes an ablation apparatus including a handpiece, an electrode extending from a handpiece distal end, a probe, a thermal sensor and an energy source. The electrode includes a distal end and a lumen, a cooling medium inlet conduit and a cooling medium exit conduit. Both conduits extend through the electrode lumen to an electrode distal end. A sidewall port, isolated from a cooling medium flowing in the inlet and outlet conduits, is formed in the electrode. The probe is at least partially positionable in the electrode lumen and configured to be advanced and retracted in and out of the sidewall aperture. The thermal sensor is supported by the probe. The electrode is coupled to an energy source.
European Application 0566726, whose disclosure is incorporated herein by reference, describes systems for ablating tissue that measure the current and voltage delivered to the associated electrode assembly and generate measured current and voltage signals. The systems divide the measured voltage signal by the measured current signal to derive a measured tissue impedance signal. The systems perform control functions based upon the measured tissue impedance signal.
International Application 2013/156896, whose disclosure is incorporated herein by reference, describes an energy application apparatus for applying energy to an object. An energy application unit applies energy to the object, wherein the energy application unit is adapted to use electrical current for applying the energy. A current measuring unit measures the electrical current used by the energy application unit and provides a signal being indicative of whether the energy is applied to the object based on the measured electrical current. The signal can be used by, for instance, a monitoring unit and/or a display unit for using and/or indicating the information whether energy is actually applied or not, without requiring a direct communication between the energy application unit and the monitoring unit and/or the display unit.
US 2003/0187430, whose disclosure is incorporated herein by reference, describes an electrode and a voltage-measurement reference device adapted to be positioned relative to a tissue load such that the load is generally located between the electrode and the reference device. A first wire and a second wire are electrically connected to the electrode. A power control system delivers RF current to the load through the first wire and measures the voltage across the load between the second wire and the reference device. The power control system measures the RF current through the first wire and determines the power delivered to the load using the measured current and voltage. The first and second wires function as thermocouple leads which, in combination with the electrode to which they are attached, form a thermocouple. The power control system monitors the voltage across the leads and determines the temperature at the electrode either during the delivery of current or alternatively, when current is not being delivered.
US 2014/0243813, whose disclosure is incorporated herein by reference, describes ablation systems and methods for providing feedback on lesion formation in real-time. The methods and systems assess absorptivity of tissue based on a degree of electric coupling or contact between an ablation electrode and the tissue. The absorptivity can then be used, along with other information, including, power levels and activation times, to provide real-time feedback on the lesions being created. Feedback may be provided, for example, in the form of estimated lesion volumes and other lesion characteristics. The methods and systems can provide estimated treatment times to achieve a desired lesion characteristic for a given degree of contact, as well as depth of a lesion being created. The degree of contact may be measured using different techniques, including the phase angle techniques and a coupling index.